Prenatal Screening Tests Explained | Prof. Dr. İkbal Kaygusuz

Prenatal Screening: Combined Test, Triple Test and NIPT

Prof. Dr. İkbal Kaygusuz Last reviewed: 25 September 2026 2 min read

In short: Prenatal screening tests estimate the risk of chromosomal conditions such as Down syndrome and some structural problems; they do not give a diagnosis. The combined test is done at 11-14 weeks with nuchal translucency, and the triple or quadruple test at 15-20 weeks. NIPT (cell-free DNA) is a more accurate screening test. If the risk is high, amniocentesis or CVS is offered for a definitive diagnosis.

Screening versus diagnosis

Screening tests calculate the likelihood of a condition and report "high" or "low" risk. Low risk does not rule out a problem and high risk does not confirm it; diagnostic tests (CVS or amniocentesis) are needed for certainty. Whether to have screening is the family's decision after counselling.

Combined test (weeks 11-14)

Maternal PAPP-A and free beta-hCG, nuchal translucency on ultrasound and maternal age are combined. The detection rate for Down syndrome is about 85-90%. The nasal bone and some organs can be assessed at the same scan.

Triple and quadruple tests (weeks 15-20)

Used when the combined test was not done or further assessment is needed. The quadruple test is more sensitive than the triple test and also gives information about neural tube defects.

NIPT (cell-free DNA)

Analyses placental DNA fragments in the mother's blood from week 10. Detection of Down syndrome exceeds 99% with a low false-positive rate. It is still a screening test: positive results must be confirmed by diagnostic testing, and NIPT does not replace the nuchal scan or the anomaly scan.

Detailed anomaly scan (weeks 18-23)

A systematic examination of the baby's brain, face, heart, abdominal organs, kidneys, spine and limbs, which detects many non-inherited structural anomalies.

Diagnostic tests

Chorionic villus sampling (CVS): a placental sample at weeks 11-14.
Amniocentesis: a sample of amniotic fluid after week 16.

Both allow chromosome analysis and detailed tests such as microarray. The procedure-related miscarriage risk is low, and decisions are made with genetic counselling.

Frequently Asked Questions

What if the combined test shows high risk?

High risk does not mean the baby is affected. After genetic counselling, NIPT or diagnostic CVS/amniocentesis are considered.

If I have NIPT, do I still need the combined test?

NIPT can replace the blood test part, but the 11-14 week scan (nuchal translucency and early anatomy) is still recommended.

Sources

ACOG Practice Bulletin No. 226: Screening for Fetal Chromosomal Abnormalities, 2020.
ISUOG Practice Guidelines: performance of 11-14-week ultrasound scan, 2023.

The information on this website is for general information only and does not replace a medical consultation.

Pregnancy2 min read

Which Pregnancy Test in Which Week? A Practical Calendar

The core schedule: first visit and blood tests at weeks 6-10, nuchal scan and combined test at 11-14, triple/quadruple test at 15-20 if needed, anomal...